JPWO2011104952A1 - Light emitting device for image display, image display device, and LED driver - Google Patents

Abstract

An object of the present invention is to provide an image display light-emitting device in which a reference current value and a PWM limiting condition are fluidly set according to the APL of an image in an area-driven image display light-emitting device controlled by PWM. Each of the light emitting elements includes a light emitting unit (5) provided corresponding to each area, a PWM control unit (44) that performs PWM control of a supply current to the light emitting elements, and a PWM value that is a duty ratio of PWM control. A control condition setting unit (45) that determines a PWM limiting condition to be limited and a reference current value that is a value of a current that flows through the light emitting element in response to the PWM control being turned on according to the APL of the image data, and sets the reference value to be updatable. ) And a PWM value calculation unit (43) that calculates a PWM value for each area based on the image data, the PWM limit condition, and the reference current value, and the PWM control unit (44) calculates the reference current value and the calculation value. The light emitting device for image display that performs PWM control based on the PWM value thus obtained.

Description

  The present invention relates to an image display light emitting device that emits light for image display, an image display device including the same, and an LED driver.

  Conventionally, various image display devices such as a liquid crystal display device and a PDP [Plasma Display Panel] display device have been devised. In general, an image display device includes a light-emitting device for image display that emits light used to display an image. The image display device displays an image by appropriately controlling the light transmission degree, intensity, and the like based on given image data.

  For example, a liquid crystal display device includes a backlight (corresponding to a part of the above-described image display light-emitting device) and a liquid crystal panel, and the light transmittance of the backlight is controlled by the liquid crystal panel so that an image is displayed. Be controlled. Various types of backlights have been devised.

  As an example, a plate-like member arranged so as to face the liquid crystal panel is divided into a plurality of areas (regions), and a light emitting element is provided in each area, which is devised as a backlight. Yes. Furthermore, a type in which light emission of light emitting elements provided in each area is controlled for each area (hereinafter sometimes referred to as “area driving type” for convenience) is disclosed in Patent Document 1. Yes.

  According to the image display device disclosed in Patent Literature 1, the brightness of the backlight (in other words, the light emission power supplied to the light emitting element of the backlight) is adjusted for each area based on the image data (that is, The brighter the corresponding image portion is, the brighter the light emitting elements belonging to that area can be made to emit light), and an image with a high contrast ratio can be obtained.

  As a light emitting element, as represented by an LED [Light Emitting Diode], a light emitting element that emits light according to a supplied current (light emission luminance changes) is mainstream. In addition, the power consumption of a backlight using such a light emitting element is generally determined by the sum of currents flowing (supplied) to the light emitting elements when the voltage applied to the light emitting elements during light emission is constant.

JP 2005-258403 A JP 2007-34251 A

  As described above, by applying the area drive type backlight, the image display apparatus can display an image with a high contrast ratio. Here, as a technique for controlling the light emission of the light emitting element, there is a technique for controlling a current (supply current) supplied to the light emitting element by PWM [Pulse Width Modulation] control.

  If such a method is adopted for an area-driven backlight using a light-emitting element that emits light according to the supply current, the duty ratio is determined for each area and the supply current is adjusted for each area. It becomes easy. Thus, PWM control is suitable as a control method for supply current in an area drive type backlight.

  When the supply current is controlled by PWM control, the amount of supply current includes the value (reference current value) of the reference current (current that flows to each light emitting element when PWM control is turned on) and the duty ratio of PWM control. Determined by the product of In general PWM control, the reference current value is fixed, and the amount of current is adjusted by changing the duty ratio.

  Here, usually, an upper limit is set for the power consumption of the backlight from the viewpoint of power saving and suppression of heat generation. Therefore, when the supply current of each area is determined, it is necessary to prevent the power consumption of the backlight from exceeding this upper limit. In this regard, when the supply current is controlled by PWM control, the supply current of each area can be determined so that the power consumption of the backlight does not exceed the upper limit.

  As an example of a technique for realizing this, the ratio of the duty ratio for each area is determined based on the image data as needed, and the ratio is maintained so that the sum of the duty ratios of each area is a predetermined upper limit. There is a method of determining the duty ratio of each area so as not to exceed the value.

The total amount of supply current is roughly
(Reference current value) x (number of LEDs per area [fixed value]) x (average value of duty ratio of each area) x (total number of areas [fixed value])
= (Reference current value) x (number of LEDs per area [fixed value]) x (sum of duty ratios in each area) (= Isum)
Can be expressed as Therefore, the power consumption of the backlight is considered even if the fluctuation of the voltage applied to the light emitting element is considered.
Isum × (maximum value of voltage applied to light emitting element [fixed value])
It is thought that it will be within the value required by.

  Therefore, if the reference current value is fixed, it is possible to limit the power consumption of the backlight by determining the upper limit value of the sum of the duty ratios of each area as in this method. In this way, by setting the PWM limit condition that limits the upper limit of the duty ratio (in this example, the upper limit value of the sum of the duty ratios), the power consumption of the backlight can be prevented from exceeding the upper limit. is there.

  By the way, when the supply current is controlled by PWM control, even when the product of the reference current value and the duty ratio are equal (that is, the supply current is equal), the reference current value is relatively large (relatively In practice, the efficiency of light emission differs when the reference current value is relatively small (relatively large duty ratio).

  More specifically, in general, even when the product of the reference current value and the duty ratio is equal, the light emission luminance of the light emitting element is higher when the reference current value is smaller (the duty ratio is larger). Become. That is, from the viewpoint of luminous efficiency, it is usually desirable to set the reference current value as small as possible.

  However, when the reference current value is set to be small, the peak luminance (the maximum luminance value of the light emitting element) is also suppressed to a small value. Therefore, depending on the situation, it is not always desirable that the reference current value is fixed to a small value.

  For example, when the APL [Average Picture Level] of an image to be displayed is relatively small, the problem that the power consumption of the backlight exceeds the upper limit hardly occurs even if the luminance of the light emitting elements in some areas is increased. Therefore, particularly when the APL of the image to be displayed is relatively small, if the reference current value can be sufficiently increased, the luminance can be increased in this way (the peak luminance is high), but the reference current value is This is difficult to do if it is fixed at a small value. Note that, for example, if the reference current value is updated to a large value in accordance with a decrease in the APL of the image, the peak luminance can be set to a high value.

  As described above, in the area drive type backlight, when the supply current is controlled by the PWM control, it is desirable that the reference current value in the PWM control is set fluidly according to the APL of the image. However, when the PWM limit condition as described above is set, the appropriate PWM limit condition also varies as the reference current value changes. Therefore, it can be said that it is desirable to set the PWM limit condition in a fluid manner as well. In the above description, the case where the light emitting device for image display is a backlight is taken as an example, but the same may be a problem in various devices in which the supply current is controlled by PWM control.

  In view of the above-described problems, the present invention is an area-driven image display light-emitting device that controls the current supplied to a light-emitting element by PWM control. An object of the present invention is to provide a light emitting device for image display that can be set fluidly according to APL. Another object of the present invention is to provide an image display device to which such a light emitting device for image display is applied.

  In order to achieve the above object, an image display light emitting device according to the present invention is provided in an image display device that displays an image based on image data, and is divided into a plurality of areas and supplied with current. A plurality of light emitting elements that emit light in response to each of the areas, a light emitting unit provided to correspond to each of the areas, and a PWM control unit that performs PWM control of a current supplied to the light emitting elements, A light emitting device for image display that emits light used for displaying the image by using an element, a PWM limiting condition that applies a certain limit to a PWM value that is a duty ratio in the PWM control, and A control condition setting unit configured to determine a reference current value, which is a value of a current flowing through the light emitting element in response to being turned on, in accordance with the APL of the image data and set the updateable value A PWM value calculation unit that calculates a PWM value for each area based on the image data, the PWM restriction condition, and the reference current value, wherein the PWM control unit calculates the reference current value and the calculated The PWM control is performed based on the PWM value.

  According to this configuration, the reference current value and the PWM limiting condition are set to be updatable according to the APL of the image data, and the light emitting element is based on the image data and the PWM value calculated based on these settings. PWM control of the current supplied to is performed. Therefore, according to the present configuration, the current supplied to the light emitting element is controlled by PWM control, and the reference current value and the PWM limiting condition in the PWM control can be set fluidly according to the APL of the image. Become.

  More specifically, the control condition setting unit may determine a limit value, which is an upper limit value of the sum of PWM values for each area, as the PWM limit condition.

  Further, in the above configuration, the control condition setting unit records in advance reference information for specifying at least one of a relationship between the APL and the limit value and a relationship between the APL and the reference current value. The limit value and the reference current value may be determined according to the reference information.

  According to this configuration, the limit value and the reference current value can be easily determined by following the reference information.

  In the above configuration, the control condition setting unit may update the setting of the limit value and the reference current value substantially simultaneously for each of one or a plurality of frames of the image data.

  According to this configuration, it is possible to maintain the consistency of both values by suppressing the update timing shift of the limit value and the reference current value, and to suppress the luminance fluctuation of the image display as much as possible. Here, “substantially simultaneous” indicates that the timing shift is within one frame (frame update period in moving image display).

  Further, in the above configuration, the PWM value calculation unit determines a ratio of the PWM values for each area based on the image data, and is determined so that a total sum of the PWM values does not exceed the limit value. The calculation may be performed according to the ratio.

  According to this configuration, it is possible to display an image with a high contrast ratio on the image display device while the current supplied to each light emitting element is limited according to the limit value set at that time. . More specifically, the light-emitting element may be an LED.

  In the above configuration, when determining the limit value and the reference current value, the control condition setting unit also determines a voltage value to be applied to the LED according to the reference current value, and adds it to the LED. The voltage value to be set may be set to the determined value.

  It is known that the voltage value required for causing an LED to emit light varies depending on the current flowing through the LED. According to this configuration, even when the fluctuation occurs due to the update of the reference current value, it is possible to appropriately cope with the fluctuation.

  Further, in the above configuration, the light emitting unit is provided with the LEDs of a plurality of colors, and the reference current value is determined for each color based on at least one of the determined reference current value and the detected temperature. It is good also as a structure provided with the color correction | amendment part to adjust.

  It is known that the emission color (color) of an LED varies depending on the current flowing through the LED and the temperature. According to this configuration, it is possible to adjust the emission color of the LEDs provided in the light emitting unit and correct the fluctuation.

  The image display device according to the present invention is configured to display an image using light emitted from the image display light emitting device having the above-described configuration. According to the image display device, it is possible to enjoy the advantages of the image display light emitting device according to the above configuration.

  The image display device according to the present invention further includes a backlight and an LCD panel that adjusts a light transmission degree for each pixel based on the image data, and supplies the light from the backlight to the LCD panel. Thus, the image display device displays an image in the display area of the LCD panel, and the image display light-emitting device having the above configuration is applied as the backlight. According to the image display device, it is possible to realize a liquid crystal display device using the image display light emitting device according to the above configuration as a backlight.

  In the above configuration, the LCD panel includes pixels of a plurality of colors, and the light transmission degree is set based on at least one of the currently set reference current value and the detected temperature. It is good also as a structure provided with the color correction | amendment part adjusted for every. According to this configuration, it is possible to adjust the degree of light transmission in the LCD panel and correct the variation in the apparent light emission color (color tone) of the LED.

  An LED driver according to the present invention supplies current to a plurality of LEDs by PWM control, and is an LED driver in which the duty ratio of the PWM control is variable for each of one or a plurality of LEDs. A reference current value that is a value of a current that flows to the LED in response to control ON is also variable, and a product that limits the product of the sum of the duty ratios and the reference current value so as not to exceed a predetermined upper limit value; To do.

  As described above, according to the light emitting device for image display according to the present invention, the reference current value and the PWM limiting condition are set to be updatable according to the APL of the image data, and based on the image data and these settings. Based on the calculated PWM value, PWM control of the current supplied to the light emitting element is performed. Therefore, the current supplied to the light emitting element is controlled by PWM control, and the reference current value and the PWM limiting condition in the PWM control can be set fluidly according to the APL of the image.

  Further, according to the image display device of the present invention, it is possible to enjoy the advantages of the light emitting device for image display according to the present invention.

It is a block diagram of the image display apparatus which concerns on embodiment of this invention. It is explanatory drawing regarding the part set to the LCD panel. It is explanatory drawing regarding the area set to the LED mounting board. It is a flowchart regarding the control procedure of the brightness | luminance of a backlight. It is explanatory drawing regarding the PWM value corresponding to each area. It is explanatory drawing regarding the corrected PWM value corresponding to each area. It is a flowchart regarding the procedure of the setting of each value regarding a control condition. It is explanatory drawing regarding the structural aspect of a LED driver. It is explanatory drawing regarding the determination procedure of 1st reference information. It is another explanatory drawing regarding the determination procedure of 1st reference information. It is explanatory drawing showing an example of the content of 1st reference information.

  An image display device (liquid crystal display device) according to an embodiment of the present invention will be described below with reference to the drawings.

[Configuration of image display device]
FIG. 1 is a configuration diagram of an image display apparatus according to the present embodiment. As shown in the figure, the image display device 9 includes an image data acquisition unit 1, an area driving circuit 2, a panel unit 3, an LED controller 4, a backlight unit 5, a temperature sensor 6, and the like.

  The image data acquisition unit 1 acquires image data for displaying an image from the outside and sends it to the area driving circuit 2. For example, when the image display device 9 is a television broadcast receiver, the image data acquisition unit 1 is provided with an antenna, a tuner, and the like, and image data (video signal) is acquired by receiving a television broadcast. Note that the image data is data for specifying the luminance of each pixel for each frame and by extension the content of a moving image (or still image).

  The area drive circuit 2 receives image data from the image data acquisition unit 1 and, based on the image data, data indicating the magnitude of current to be supplied to the backlight LED (hereinafter referred to as “LED data”). Generate. The higher the brightness in the image data, the more LED data is generated to represent a larger current (ie, to make the LED emit light brighter). The LED data is in the form of a 12-bit digital signal, for example, and is sent to the LED controller 4 (adjustment circuit 41).

  The area driving circuit 2 generates data representing the APL of the image in each frame (hereinafter referred to as “APL data”) based on the image data, and sends the data to the LED controller 4 (control condition setting circuit 45). Furthermore, the area driving circuit 2 also generates LCD data that is light transmittance data of each pixel of the LCD panel 11 based on the image data. The generated LCD data is supplied to the panel unit 3.

  The panel unit 3 is a unit having a function as a panel for displaying an image, and includes an LCD controller 32, an LCD driver 33, and the like in addition to the LCD panel 31. The LCD panel 31 has a rectangular shape in plan view, and is configured such that a pair of glass substrates are bonded together with a predetermined gap therebetween, and liquid crystal is sealed between the glass substrates.

  In addition, one glass substrate is provided with a switching element (for example, a thin film transistor) connected to a source wiring and a gate wiring orthogonal to each other, a pixel electrode connected to the switching element, an alignment film, and the like. The glass substrate is provided with a color filter in which colored portions of RGB (red, green, and blue) are arranged in a predetermined arrangement, a common electrode, an alignment film, and the like.

  Further, a polarizing plate is further disposed on the outside of both substrates. In the present embodiment, it is assumed that 1920 × 1080 dot color pixels (RGB pixels) are formed in the display area of the LCD panel 31. However, the number and types of pixels may be other modes.

  The display area of the LCD panel 31 is equally divided into 24 (= 6 × 4) parts (first part to 24th part) as shown in FIG. Note that the number n (n is an integer from 1 to 24) shown in FIG. 2 indicates that the part is the n-th part. For example, the first part is a portion to which pixels of 320 (= 1920/6) × 270 (= 1080/4) dots belong in the upper left of the display area.

  Note that the term “part” here is defined for convenience in order to indicate a part of the display area. In the present embodiment, the number of parts is 24, but this is an example, and it may be more or less. As will be described in detail later, the LED mounting board 53 disposed on the back side of the LCD panel 31 has 24 areas (each area has at least one LED mounted thereon) so as to correspond to each part of the LCD panel 31. The light emission state of the LED is controlled for each area.

  Returning to FIG. 1, the LCD controller 32 generates a signal for driving the LCD driver 33 in accordance with the LCD data supplied from the area driving circuit 2, and sends the signal to the LCD driver 33. The LCD driver 33 switches the state of each switching element provided in the LCD panel 31 based on the signal received from the LCD controller 32.

  As a result, the voltage of each pixel electrode provided in the LCD panel 31 is adjusted according to the image data, and as a result, the degree of light transmission in each pixel is adjusted. As a result, the image display device 9 illuminates the backlight from the back side of the LCD panel 31 (by giving the backlight light to the LCD panel 31), and displays an image on the display area of the LCD panel 31.

  The LED controller 4 includes an adjustment circuit 41, a PWM value calculation circuit 42, a PWM value limiter circuit 43, an LED control signal generation circuit 44, a control condition setting circuit 45, and the like. Although described in detail later, the current supplied to the LED 52 in the backlight 5 is controlled by PWM control. The LED controller 4 plays a role of generating an LED control signal necessary for the PWM control and sending it to the backlight unit 5 as described below.

  The adjustment circuit 41 performs various adjustments such as white balance and temperature correction on the LED data received from the area driving circuit 2, and sends it to the PWM value calculation circuit 42. In the PWM value calculation circuit 42, information on the reference current value (the value of the current passed through each LED 52 in response to the PWM control being turned on) Ist is set (recorded) so as to be updatable.

  Then, the PWM value calculation circuit 42 is based on the LED data received from the adjustment circuit 41 and the currently set reference current value Ist, and the duty ratio in the PWM control (hereinafter sometimes referred to as “PWM value”). Is calculated for each area. Further, the PWM value calculation circuit 42 also calculates the sum of the PWM values for each area, and transmits the calculation result to the PWM value limiter circuit 43.

  The PWM value limiter circuit 43 sets (records) the information of the PWM limit value so as to be updatable, and limits the PWM value for each area so that the sum of the PWM values does not exceed the PWM limit value. Information on the PWM value for each area to which such restriction is applied is sent to the LED control signal generation circuit 44.

  In the LED control signal generation circuit 44, information on the reference current value Ist and the LED voltage value Vf (the voltage value required for causing each LED 52 to emit light appropriately) is set (recorded) in an updatable manner. The LED control signal generation circuit 44 generates a PWM signal for each area according to the PWM value for each area received from the PWM value limiter circuit 43. Then, the LED control signal generation circuit 44 outputs an LED control signal including information on the PWM signal for each area, the currently set reference current value Ist, and the currently set LED voltage value Vf to the backlight unit 5. To send.

  Based on the APL data received from the area driving circuit 2, the control condition setting circuit 45 is configured to control each value (PWM limit value, reference current value Ist, and LED voltage) for each circuit (42 to 44). The value Vf) is updated accordingly. The operation content of the LED controller 4 will be described in detail again.

  The backlight unit 5 includes an LED driver 51, an LED 52, an LED mounting substrate (LED panel) 53, and optical members (not shown) necessary for forming a backlight such as a diffusion plate and an optical sheet, and the like. Functions as a backlight for the device. The LED driver 51 has one or a plurality of control channels to which the LEDs 52 are connected. The LED driver 51 drives the LEDs 52 connected to each control channel according to the LED control signal supplied from the LED controller 4.

  That is, the LED driver 51 supplies the current of the reference current value Ist to the LED 52 in the area corresponding to the PWM signal during the period in which the PWM signal is at the H level (ON), and turns on the LED 52. At this time, the LED driver 51 applies a voltage of the LED voltage value Vf to the LED 52.

  Normally, when the reference current value Ist increases, the LED voltage value Vf increases. When the reference current value Ist decreases, the LED voltage value Vf decreases (this is controlled by the LED control signal). . Therefore, when the reference current value Ist is increased from the current time, the LED driver 51 first increases the voltage applied to the LED 52 and then increases the reference current value Ist. When the reference current value Ist is decreased from the current time, the LED driver 51 first After the reference current value Ist is lowered, the voltage applied to the LED 52 is lowered.

  On the other hand, the LED driver 51 stops the supply of current to the LEDs 52 in the area corresponding to the PWM signal and turns off the LED 52 during the period in which the PWM signal is at the L level (off). Each of the LEDs 52 is connected to a different control channel at least for each area. Thereby, the lighting / extinguishing of the LED 52 can be controlled for each area.

  The LED 52 is formed as an LED chip, for example, and is disposed on the mounting surface of the LED mounting substrate 53 to function as a light source of a backlight for the LCD panel 31. The LED mounting substrate 53 is attached to the back side of the LCD panel 31 so that the mounting surface faces the LCD panel 31.

  As described above, the LED mounting board 53 is divided into 24 areas corresponding to the parts of the LCD panel 31 as shown in FIG. Note that the number n shown in FIG. 3 indicates that the part is the nth area. The nth area in the LED mounting substrate 53 corresponds to the nth part in the LCD panel 31.

  The LED 52 forms an LED unit in which light emitting elements of RGB (red, green, and blue) are gathered, and at least one LED unit is disposed in each area of the LED mounting substrate 53. Each LED unit emits light of each color of RGB to emit light substantially white as a whole. In addition, about the form (a kind, a color, a combination, etc.) of LED52, another aspect may be sufficient. For example, a white LED may be used instead of the LED unit described above, or an LED unit in which LEDs that emit light of RGBW (red, green, blue, and white) are gathered may be used.

  Note that the nth area of the LED mounting substrate 53 is disposed almost directly behind the nth part of the LCD panel 31. Therefore, the light emission intensity of the LED unit in the nth area (in other words, the magnitude of the supplied light emission power) has a particularly great effect on the brightness of the image display in the nth part.

  The temperature sensor 6 is formed by a thermistor or a thermocouple, for example, and is attached to the LED mounting substrate 53 (near the LED 52). Thereby, the temperature sensor 6 detects the temperature in the vicinity of the LED 52. Information on the detected temperature is transmitted to the area driving circuit 2 and used for color correction processing in image display.

  The video display device 9 has the above-described configuration, generates LCD data and LED data based on the image data acquired by the image data acquisition unit 1, and transmits the light transmittance of the LCD panel 31 and the LED 52 (backlight). An image is displayed by controlling the brightness of the image. Here, the control procedure of the luminance of the backlight in the video display device 9 will be described in more detail below.

[Backlight brightness control procedure]
Next, the backlight luminance control procedure will be described with reference to the flowchart shown in FIG.

  The image data acquisition unit 1 acquires image data through reception of a television broadcast or the like (step S1), and the acquired image data is input to the area driving circuit 2. In response to this, the area drive circuit 2 generates LED data of each area (first area to 24th area) based on the image data (step S2). The LED data represents the total amount of current to be supplied to the LED 52 for each area.

  In the present embodiment, the LED data of each area is determined based on the maximum luminance value of the image data corresponding to each area. That is, there are a plurality of pixels in each part of the LCD panel 31 corresponding to each area. Therefore, it is assumed that the LED data of each area is determined based on the maximum value of the luminance related to the plurality of pixels.

  In addition, the determination method of the LED data is not limited to this, and may be determined based on, for example, an average value of luminance related to a plurality of pixels corresponding to each area. In the present embodiment, the LED data of each area is determined in accordance with the frame period of the acquired image data (that is, every frame).

  However, the cycle in which the LED data is determined is not limited to such a mode, and may be every 5 frames or every 30 frames, for example. When the acquired image data represents a still image, the LED data may be determined only when the screen changes.

  Thereafter, the adjustment circuit 41 of the LED controller 4 receives the LED data from the area drive circuit 2, and performs adjustments such as white balance and temperature correction on the LED data (step S3). Thereafter, the PWM value calculation circuit 42 calculates a PWM value corresponding to each area based on the adjusted LED data and the reference current value Ist (step S4).

The PWM value of each area is
It is calculated by an expression represented by (value of LED data) / {(reference current value Ist) × (number of LEDs per area)}. That is, for each area, the PWM value is calculated so that the sum of the currents supplied to the LED 52 by PWM control is equal to the value of the LED data. Even if the LED data values are the same, the larger the reference current value Ist, the smaller the PWM value is calculated, and the smaller the reference current value Ist, the larger the PWM value is calculated.

  According to the process of step S4, for example, the PWM value corresponding to each area is calculated to be the value shown in FIG. Note that the number n in parentheses in FIG. 5 represents the n-th area, and therefore, for example, the PWM value of the seventh area is 100 (%). According to FIG. 5, the PWM value corresponding to each area is calculated as one of 0 (%), 50 (%), and 100 (%).

The PWM value calculation circuit 42 calculates the sum total of the PWM values corresponding to the calculated areas (step S5). According to the process of step S5, for example, when the PWM value corresponding to each area is as shown in FIG.
PWMsum = (PWM value of the first area) + (PWM value of the second area) +
... + (PWM value of 24th area)
= 1600 (%) (Area average is 66.7%)
Is calculated.

  Next, the PWM value limiter circuit 43 determines whether or not the total PWM sum of the calculated PWM values exceeds the currently set power limit value (step S6). As a result, if it is determined that it does not exceed (N in step S6), the PWM value limiter circuit 43 sends the PWM value information corresponding to each area to the LED control signal generation circuit 44 as it is.

  However, if it is determined that it has exceeded (Y in Step S6), the PWM value limiter circuit 43 causes the PWM value sum PWMsum to be equal to or less than the PWM limit value (in other words, the PWM value sum PWMsum). The PWM value corresponding to each area is corrected (step S7). The procedure for correcting the PWM value corresponding to each area is as follows.

  First, the PWM value limiter circuit 43 calculates a limiting rate α, which is a value obtained by dividing the PWM limit value by the total PWM value of the PWM values. For example, when the PWM value corresponding to each area is as shown in FIG. 5 (therefore, the total PWM sum of PWM values is 1600 (%)) and the PWM limit value is set to 1200 (%), the limiting rate α is calculated as 1200/1600 = 0.75.

  Thereafter, the PWM value limiter circuit 43 corrects the PWM value corresponding to each current area by multiplying the PWM value corresponding to each current area by the limiting rate α. Thereby, the information of the PWM value corresponding to each corrected area is generated. For example, when the current PWM value corresponding to each area is as shown in FIG. 5 and the limiting rate α is 0.75, the PWM value corresponding to each corrected area is shown in FIG. It becomes the value shown.

  As a result, the sum PWMsum of the corrected PWM values is equal to or less than the PWM limit value (in this embodiment, equal to the PWM limit value). As a result, the upper limit of the PWM value sum PWMsum is limited to the PWM limit value. Is done. Thus, the PWM limit value can also be regarded as a condition for adding a certain limit to the PWM value (PWM limit condition). However, the PWM limiting condition may be other than this. Further, the PWM value limiter circuit 43 sends the PWM value information corresponding to each corrected area to the LED control signal generation circuit 44.

  Note that the PWM value corresponding to each corrected area is a value obtained by dividing the value before correction uniformly by the limiting rate α. Therefore, the ratio of the corrected PWM value for each area is maintained as it is before the correction. In other words, the calculation of the PWM value for each area is first determined based on the image data so that the ratio of the PWM values for each area is determined and the total PWM sum of the PWM values does not exceed the PWM limit value. According to the ratio. As a result, the image display device 9 can maintain image display with a high contrast ratio (with a sense of peak luminance) as much as possible while limiting the power consumption of the backlight.

  Next, the LED control signal generation circuit 44 generates a PWM signal corresponding to each area in accordance with the PWM value information of each area received from the PWM value limiter circuit 43. Then, in addition to this PWM signal, an LED control signal including information on the currently set reference current value Ist and the currently set LED voltage value Vf is generated and sent to the backlight unit 5 (step) S8). Thereby, the current supplied to the LEDs 52 belonging to each area is controlled (by PWM control) in accordance with the PWM signal corresponding to that area.

[Updating each value related to control conditions]
Each value (PWM limit value, reference current value Ist, and LED voltage value Vf) related to the backlight control condition set in each circuit (42 to 44) is updated mainly by the operation of the control condition setting circuit 45. It has come to be. The update procedure will be described below with reference to the flowchart shown in FIG.

  When the control condition setting circuit 45 acquires APL data for one frame of image data from the area driving circuit 2 (step S11), an operation for realizing the update (hereinafter referred to as “update operation” for convenience). Execute.

  The cycle in which the update operation is executed is not limited to such a mode, and may be every 5 frames or every 30 frames, for example. If the acquired image data represents a still image, the update operation may be executed only when the screen changes. For example, when the update operation is executed every 5 frames, the APL data used for the update operation may be the APL data at that time (that is, APL data for one frame), and the latest 5 frames. The APL data may be averaged.

  Note that if the update timing of the PWM limit value is different from the update timing of the reference current value Ist, these values may not be consistent, and the user may feel uncomfortable due to luminance fluctuations in image display. For this reason, the updating of these values is executed substantially simultaneously, that is, so that the timing shift is within one frame (the frame updating cycle in moving image display).

  Further, as an update operation, the control condition setting circuit 45 first determines a reference current value Ist and a PWM limit value based on the acquired APL data (step S12). The control condition setting circuit 45 includes information for specifying the relationship between the APL data, the reference current value Ist, and the PWM limit value (for example, a function representing the relationship or LUT [Look Up Table]). "Referred to as" first reference information ") is recorded in advance. The control condition setting circuit 45 refers to the first reference information and determines the reference current value Ist and the PWM limit value. Note that how the contents of the first reference information are determined will be described later in the section “About the contents of the first reference information”.

  Next, the control condition setting circuit 45 determines the LED voltage value Vf based on the determined reference current value Ist (step S13). The control condition setting circuit 45 includes information for specifying the relationship between the reference current value Ist and the LED voltage value Vf (for example, a function representing the relationship or an LUT, and hereinafter referred to as “second reference information”). Are recorded in advance, and the control condition setting circuit 45 determines the LED voltage value Vf with reference to the second reference information.

  As for LEDs, it is known that the LED voltage value Vf changes with the flowing current (in general, the larger the current, the larger the LED voltage value Vf), and the flowing current and the LED voltage value Vf. Can be specified in advance (for example, by actual measurement at the design stage of the image display device 9). Therefore, it is possible to record the second reference information in the control condition setting circuit 45 in advance.

  Note that the LED voltage value Vf also varies depending on the temperature of the LED. Therefore, the detection result of the temperature sensor 6 is also transmitted to the control condition setting circuit 45, and the LED voltage value Vf is determined based not only on the determined reference current value Ist but also on the detection result of the temperature sensor. You may be made to do. In this case, the second reference information is provided as information for specifying the relationship between the reference current value Ist and the LED voltage value Vf at each temperature.

  At the time when the operation of step S13 is completed, based on the newly acquired APL data, each value related to the control condition, that is, each of the PWM limit value, the reference current value Ist, and the LED voltage value Vf is newly Has been determined. Therefore, the control condition setting circuit 45 sends information on these newly determined values to the circuits (42 to 44).

  Thereby, the setting of each value related to the control condition in each circuit (42 to 44) is updated to the one newly received from the control condition setting circuit 45 (step S14). Thereafter, the setting of each value related to the control condition updated this time is maintained until the next update is performed.

  In the above description, for ease of understanding, the light emission control is performed in the same manner for each LED 52. However, the light emission control of the LED 52 may be performed separately for each color (RGB), for example. . Various data and values related to LED light emission control (LED data, PWM value, PWM limit value, reference current value Ist, LED voltage value Vf, etc.) are provided separately for each color, and the series of operations described above. By performing (steps S1 to S8, steps S11 to S14) for each color, the light emission control of the LED 52 for each color is realized.

  FIG. 8 shows an example of the configuration of the LED driver 51 when the light emission control of the LED 52 is performed separately for each color (RGB). In this aspect, the LED driver 51 is provided with a power supply circuit (8R to 8B) corresponding to each of RGB and a control component 51a corresponding to each of the LED units provided on the LED mounting board 53. The LED driver 51 receives an LED control signal including information on the PWM signal for each color area, the reference current value Ist for each color, and the LED voltage value Vf for each color from the LED controller 4 side.

  The power supply circuit 8R corresponding to red (R) receives information on the LED voltage value Vf of red (R) via a DAC (Digital Analog Converter) (not shown) and generates a voltage corresponding to the information. Similarly, the power supply circuits (8G, 8B) corresponding to green (G) and blue (B) also receive information on the LED voltage value Vf of green (G) and blue (B), respectively, and voltages corresponding thereto Is generated.

  The control component 51a includes transistors (QR to QB) whose collectors are connected to the power supply circuits (8R to 8B) and whose emitters are grounded, power supply circuits (8R to 8B), and transistors (QR to QB). Each switch (SWR to SWB) for switching between conduction and non-conduction with the above is provided. Also, one end and the other end of the switch SWR are connected to the red (R) LED 52 in the LED unit, and one end and the other end of the switch SWG are connected to the green (G) LED 52 in the LED unit. The other end is connected to the blue (B) LED 52 in the LED unit.

  The transistor QR corresponding to red (R) adjusts the current flowing between the collector and the emitter according to the information of the reference current value Ist of red (R). Similarly, the transistors (QG, QB) corresponding to green (G) and blue (B) also receive the information on the reference current value Ist of green (G) and blue (B), respectively, and the collector- Adjust the current flowing between the emitters.

  The switch SWR corresponding to red (R) is switched between conductive / non-conductive (ON / OFF) in accordance with the red (R) PWM signal. Similarly, the switch SWR corresponding to green (G) and blue (B) is switched between conductive / non-conductive (ON / OFF) according to the PWM signals of green (G) and blue (B).

  With such a configuration, adjustment of the voltage applied to the LED 52 is realized mainly by each power supply circuit (8R to 8B), and adjustment of the magnitude of the current flowing through the LED 52 is mainly performed to each transistor (QR to QB). It is realized by. Further, on / off switching of PWM control is realized mainly by each switch (SWR to SWB). The configuration mode shown here is an example, and the configuration of the LED driver 51 may be another mode.

[Contents of first reference information]
The first reference information described above is recorded in the control condition setting circuit 45 after its contents are determined in advance, for example, at the design stage of the image display device 9. How the content of the first reference information is determined will be described below with a specific example.

  First, for the image display device 9, the setting of the PWM limit value is fixed, and the correspondence between the APL of the image and the peak luminance of the LED 52 when the image is displayed is investigated. The investigation is performed, for example, by preparing data of each test image having various values of APL and measuring the peak luminance of the LED 52 when these test images are sequentially displayed. The Such an investigation is performed for a plurality of PWM limit values.

In this investigation, the reference current value Ist is set according to the PWM limit value at that time so that, for example, the following expression (1) is satisfied.
(Reference current value Ist) × (number of LEDs 52 per area) × (PWM limit value) × (maximum value of LED voltage Vf) = (upper limit value of power consumption of backlight) (1)
Note that “the number of LEDs per area” and “the maximum value of the LED voltage Vf” are fixed values that are known in advance. As for the “upper limit value of power consumption of the backlight”, a predetermined value is defined as a standard from the viewpoint of power saving and heat generation suppression.

  That is, the reference current value Ist is such that the total power consumption of the LEDs 52 does not exceed the “upper limit value of power consumption of the backlight” and that the reference current value Ist does not become unnecessarily small. Is set. When the LEDs 52 are controlled to emit light for each color, for the same purpose, the sum of the power consumption of the LEDs 52 for each color may not exceed the “upper limit value of power consumption of the backlight”. The reference current value Ist is set.

  When the above-described investigation is performed for each of the PWM limit values C1, C2, and C3 (where C1 <C2 <C3), for example, an investigation result as shown in FIG. 9 is obtained. In the graph shown in FIG. 9, the horizontal axis represents APL (%), and the vertical axis represents the peak luminance of the LED 52. The graph shows a case where the PWM limit value is fixed to C1, a dotted line, a case where the PWM limit value is fixed to C2, a broken line, and a case where the PWM limit value is fixed to C3, a dotted line. According to FIG. 9, the PWM limit value at which the peak luminance is maximum varies depending on APL.

  Therefore, based on this investigation result, a case is assumed in which the PWM limit value is adjusted so that the peak luminance of the LED 52 becomes maximum for each APL. Note that when such adjustment is made, the correspondence between the APL and the peak luminance of the LED 52 is, for example, as shown by a solid line in FIG. In this case, the correspondence between the APL and the PWM limit value is obtained.

  According to this correspondence, a PWM limit value that maximizes the peak luminance can be obtained for each APL while suppressing the power consumption of the backlight within an allowable range. Therefore, based on the correspondence obtained in this way, various restrictions (for example, a fixed lower limit is set for the PWM limit value) according to the actual situation, or a predetermined correction is performed. The correspondence information obtained in this way is employed as the first reference information.

  If the correspondence between APL and the PWM limit value is determined, the correspondence between APL and the basic .3 quasi-current value Ist is also determined according to the above-described equation (1). Therefore, the correspondence between the APL and the reference current value Ist is also adopted as the first reference information.

  Through the procedure so far, for example, information shown in FIG. 11 can be obtained as the first reference information for specifying the relationship between the APL, the PWM limit value, and the reference current value Ist. However, the procedure described above is merely an example, and the contents of the first reference information can be determined by various other procedures.

  When the relationship between the reference current value Ist and the PWM limit value (for example, the relationship represented by the above-described equation (1)) is set in advance, the first reference information is the relationship between the APL and the PWM limit value. May be information that specifies only the relationship between the APL and the reference current value Ist. Even in this case, if the APL is specified, it is possible to specify both the reference current value Ist and the PWM limit value.

[Color correction through the panel unit]
Incidentally, it is generally known that the actual emission color (wavelength of light) of an LED changes depending on the temperature of the LED and the magnitude of a flowing current. The degree of change differs depending on the type of LED (for example, RGB color), and the degree of change is particularly large in green (G) LEDs.

  Therefore, in the image display device 9 that uses the LED 52 as the light source of the backlight, the color of the image display changes depending on the temperature of the LED 52 and the magnitude of the flowing current. For example, when an LED unit in which LEDs of RGB colors are gathered in the backlight (in an ideal state, the LED emits white as a whole), the RGB colors cannot be balanced and the LED unit emits light to the original color. It disappears and the color of the image display changes. Therefore, it is desirable that the change is corrected in the image display device 9. An example of a method for realizing such color correction through the panel unit 3 will be described below.

  As described above, the area driving circuit 2 generates LCD data and sends it to the panel unit 3, and the degree of light transmission in the LCD panel 31 is set according to the LCD data. Therefore, the LCD data is generated so that the color of the image display is corrected (for the pixel of the color whose luminance should be reduced, the degree of light transmission is reduced).

  More specifically, information of the currently set reference current value Ist (representing the magnitude of the current flowing through the LED 52) is transmitted to the area driving circuit 2. Then, the area driving circuit 2 comprehensively considers the detection information of the temperature sensor 6 and the information of the reference current value Ist (however, only one of the information may be considered), and the image display LCD data is generated so as to correct the color tone. In other words, the LCD data is generated so that the light transmission in the LCD panel 31 is corrected for each color based on at least one of the currently set reference current value Ist and the detected temperature. deep.

  Since it is known in advance how much the LED temperature and the magnitude of the flowing current change and how much the emission color of the LED changes, it is possible to generate LCD data in this way. Thereby, it is possible to realize the color correction in the image display through the panel unit 3.

[Color correction through the backlight unit]
If an LED unit (see FIG. 3) made up of RGB LEDs is used as the light source of the backlight, and values such as the reference current value Ist are set for each color, the color in the image display It is also possible to achieve taste correction through the backlight unit 5. An example of a method for realizing such correction will be described below.

  As described above, the control condition setting circuit 45 determines a value such as the reference current value Ist according to the APL data, and the setting of the reference current value Ist and the like in each circuit (42 to 44) is set to the determined value. Updated. Therefore, the reference current value Ist is determined so that the color of the image display is corrected (for the LED 52 of the color whose luminance should be reduced, the flowing current is reduced).

  More specifically, the detection information of the temperature sensor 6 is transmitted to the control condition setting circuit 45 in advance. Then, after the control condition setting circuit 45 determines the reference current value Ist according to the APL data (see step S12), the determined reference current value Ist and the detection information of the temperature sensor 6 are comprehensively considered (however, The reference current value Ist is corrected for each color so that the color of the image display is corrected.

  Thereby, it is possible to realize the color correction in the image display through the panel unit 3. The reference current value Ist is preferably corrected so that the reference current value Ist of any color is smaller than the current value (that is, does not exceed the current value). In this way, it is possible to avoid a situation where the power consumption of the backlight exceeds the allowable range due to the correction of the reference current value Ist.

[Specifications of LED driver]
By the way, generally, in an LED driver, required structural conditions and the like differ depending on the maximum supply power (maximum value of power that can be supplied) which is one of the characteristics. Specifically, an LED driver having a relatively large maximum power supply can supply a large amount of power. However, a structure that can withstand heat generation is required, so that downsizing is difficult.

  On the other hand, an LED driver having a relatively small maximum power supply cannot supply a large amount of power, but since it has been known in advance that no large amount of heat is generated, downsizing is facilitated. When an LED driver is employed as a component of various devices, an LED driver with an appropriate maximum supply power is selected according to the performance and application of the device.

  Here, from the viewpoint of the maximum supply power, an LED driver suitable for the image display device 9 of the present embodiment is proposed. The LED driver supplies current to the LED by PWM control, and is automatically limited so that the sum of supplied currents does not exceed a predetermined value (hereinafter referred to as “current limiting specification” for convenience). It is). The specific configuration and the like of the current-limiting LED driver are as follows.

  The LED driver of the current limit specification has a plurality of control channels to which one or a plurality of LEDs are connected, and the duty ratio of PWM control is set for each control channel (that is, for each one or a plurality of LEDs). It is variable. Each control channel supplies a reference current (common to each control channel) to each connected LED in response to the PWM control being turned on. That is, the current that each control channel passes in response to the PWM control being turned on is (reference current) × (the number of LEDs connected to the control channel).

  Further, in the current-limited specification LED driver, the value of the reference current is also variable. The LED driver of the current limiting specification is supplied with data that can specify the duty ratio for each control channel and the value of the reference current from the outside, for example, and basically supplies current to each LED according to this data.

  However, the upper limit value of the product of the reference current value and the sum of the duty ratios is determined for the current limiting specification LED driver, and the reference current is limited according to this upper limit value. That is, the LED driver of the current limit specification calculates the sum of the duty ratios of the respective control channels, and limits the reference current value to a value (limit value) obtained by dividing the upper limit value by the calculated value. The LED driver assumes that the actual reference current value is equal to or less than the limit value, even if data that causes the reference current value to exceed the limit value is input.

  Note that the LED driver of the current limiting specification may limit the sum of the duty ratios instead of limiting the reference current. In this case, after the value of the reference current is specified, the LED driver limits the total duty ratio to a value (limit value) obtained by dividing the above-described upper limit value by the value of the reference current. The LED driver corrects the duty ratio so that the sum of the duty ratios is equal to or less than the limit value even if the sum is calculated to exceed the limit value.

  In any case, the sum of the supply currents is represented by (reference current value) × (number of LEDs connected to each control channel [assuming at least the maximum value is determined)] × (sum of duty ratios). Therefore, if the upper limit value of the product of the reference current value and the sum of the duty ratios is determined, the upper limit of the sum of the supply currents is limited.

  According to the current limiting specification LED driver that operates in this manner, when the sum of the duty ratios is small, the value of the reference current can be increased, and the peak luminance of the LED can be increased. Further, according to the LED driver, since the sum of the supply currents is limited (if the sum of the duty ratios is large, the value of the reference current does not increase), the LED in which the value of the reference current is fixed to a large value The maximum power supply is smaller than that of the driver. Therefore, the LED driver does not require a structure that can withstand heat generation, and can be easily reduced in size and cost.

  As described above, the LED driver of the current limit specification is fixed to a value with the advantage of the LED driver in which the value of the reference current is fixed to a small value (small heat generation and easy miniaturization) and the value of the reference current is large. The advantages of the LED driver (the peak luminance of the LED can be increased) are combined. Therefore, for example, if an LED driver with a current limiting specification is applied to the image display device 9 of the present embodiment, the image display device 9 can be reduced in size and cost while maintaining the original function of the image display device 9. It becomes easy.

  The LED driver having the current limit specification described above is suitable for the image display device 9 of the present embodiment in which the reference current value Ist and the PWM limit value are updated as needed, but is also applicable to other various devices using LEDs. Is possible.

[Summary]
The image display device 9 according to the present embodiment described above is a device that emits a backlight (light-emitting device for image display) including the area drive circuit 2, the LED controller 4, and the backlight unit 5 as main components. It has. The image display light-emitting device is divided into a plurality of areas, and each of the plurality of LEDs 52 (light-emitting elements) that emit light according to the supplied current is provided so as to correspond to each of the areas. The backlight unit 5 (light emitting unit) and a functional unit (PWM control unit) that PWM-controls the current supplied to the LED 52 are provided.

  The image display light-emitting device also includes a PWM limiting condition that applies a certain limit to the duty ratio (PWM value) in the PWM control, and the value of the current that flows to the LED 52 when the PWM control is turned on (reference current value Ist). ) Is determined according to the APL of the image data and is set to be updatable, and the PWM value for each area based on the image data, the PWM limit condition, and the reference current value Ist And a function unit (duty ratio calculation unit).

  In the present embodiment, the PWM limit value, which is the upper limit value of the sum of the PWM values for each area, is determined as the PWM limit condition. However, the PWM limiting condition may be another mode. The PWM control unit performs PWM control based on the reference current value Ist and the calculated PWM value.

  Therefore, according to the light emitting device for image display, the reference current value Ist and the PWM limiting condition are set to be updatable according to the APL of the image data, and the PWM value calculated based on the image data and these settings Based on the above, PWM control of the current supplied to the LED 52 is performed.

  Thus, according to the light emitting device for image display, the current supplied to the LED 52 is controlled by the PWM control, and the reference current value Ist and the PWM limiting condition in the PWM control are fluidized according to the APL of the image. It is possible to set. As a result, by appropriately preparing the first reference information so that the LED 52 emits light efficiently according to APL, an image display light emitting device that emits light efficiently is realized.

  When the reference current value Ist is changed, the LED voltage Vf and the LED emission color (light wavelength) also change. However, as already described, according to the light emitting device for image display of the present embodiment, it is possible to appropriately cope with these fluctuations and maintain good image display.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this content. The embodiments of the present invention can be variously modified without departing from the gist of the present invention.

  The present invention can be used for various image display devices.

DESCRIPTION OF SYMBOLS 1 Image data acquisition part 2 Area drive circuit 3 Panel unit 4 LED controller 5 Backlight unit 6 Temperature sensor 8R Power supply circuit corresponding to red (R) 8G Power supply circuit corresponding to green (G) 8B Corresponding to blue (B) Power supply circuit 9 Image display device 31 LCD panel 32 LCD controller 33 LCD driver 41 Adjustment circuit 42 PWM value calculation circuit 43 PWM value limiter circuit 44 LED control signal generation circuit 45 Limit condition setting circuit 51 LED driver 51a Control component 52 LED (light emitting element) One form)
53 LED mounting board SWR Switch corresponding to red (R) SWG Switch corresponding to green (G) SWB Switch corresponding to blue (B) QR Transistor corresponding to red (R) QG Transistor corresponding to green (G) QB Transistor corresponding to blue (B)

Claims (12)

It is provided in an image display device that displays an image based on image data,
A plurality of light emitting elements that are divided into a plurality of areas and each of the plurality of light emitting elements that emit light according to a supplied current corresponds to each of the areas;
A PWM control unit that PWM-controls a current supplied to the light emitting element,
A light emitting device for image display that emits light used for displaying the image using the light emitting element,
A PWM limit condition for applying a fixed limit to a PWM value that is a duty ratio in the PWM control, and a reference current value that is a value of a current that flows through the light-emitting element in response to the PWM control being turned on are set as an APL of the image data. A control condition setting unit that is determined according to and set to be updatable,
A PWM value calculation unit that calculates a PWM value for each area based on the image data, the PWM limit condition, and the reference current value;
The PWM control unit
A light emitting device for image display, wherein the PWM control is performed based on the reference current value and the calculated PWM value. The control condition setting unit
The light emitting device for image display according to claim 1, wherein a limit value that is an upper limit value of a sum of PWM values for each area is determined as the PWM limit condition. The control condition setting unit
Reference information for specifying at least one of the relationship between the APL and the limit value and the relationship between the APL and the reference current value is recorded in advance,
The light emitting device for image display according to claim 2, wherein the limit value and the reference current value are determined according to the reference information. The control condition setting unit
3. The light emitting device for image display according to claim 2, wherein the setting of the limit value and the reference current value is updated substantially simultaneously for each one or a plurality of frames of the image data. The PWM value calculation unit
Based on the image data, the ratio of the PWM value for each area is determined,
The light emitting device for image display according to claim 2, wherein the calculation is performed so that a sum of PWM values does not exceed the limit value and according to the determined ratio.   The light emitting device for image display according to claim 2, wherein the light emitting element is an LED. The control condition setting unit
When determining the limit value and the reference current value, the value of the voltage to be applied to the LED is also determined according to the reference current value,
The light emitting device for image display according to claim 6, wherein the value of the voltage applied to the LED is set to the determined value. The light emitting device for image display according to claim 6 or 7, wherein the light emitting unit includes the LEDs of a plurality of colors.
A light emitting device for image display, comprising: a color correction unit that corrects the reference current value for each color based on at least one of the determined reference current value and detected temperature.   An image display device, wherein an image is displayed using light emitted from the light emitting device for image display according to claim 1. With backlight,
An LCD panel that adjusts the degree of light transmission for each pixel based on the image data,
An image display device that displays an image on a display area of the LCD panel by applying light from the backlight to the LCD panel,
An image display device, wherein the image display light-emitting device according to claim 2 is applied as the backlight. The image display device according to claim 10, wherein the LCD panel includes pixels of a plurality of types of colors.
An image display device comprising: a color correction unit that corrects the degree of light transmission for each color based on at least one of the currently set reference current value and detected temperature. An LED driver that supplies current to a plurality of LEDs by PWM control, and the duty ratio of the PWM control is variable for each one or a plurality of LEDs,
The reference current value, which is the value of the current that flows through the LED in response to the turning on of the PWM control, is also variable.
An LED driver, wherein a product of the sum of the duty ratios and the reference current value is limited so as not to exceed a predetermined upper limit value.